Fracture toughness of resin based composites

A study has been made of several composite systems based on polyester resin matrix, investigating the influence of various parameters on their fracture behaviour. This included the effects of such variables as the specimen geometry, fibre and filler volume fractions and the particle size of heavy metal dispersions within the resin itself or the resin reinforced with glass fibres. Different methods of fabrication have been attempted and tests were carried out on each polyester particle and/or fibre dispersion combination in order to examine their fracture resistance. In two phase composite systems, the powder dispersions showed less influence on the resulting fracture toughness than the fibre reinforcement. The toughness of three phase particle filled fibre reinforced composites were also primarily governed by the fibre reinforcement. Mechanisms which may have contributed to the fracture behaviour of these composites have been considered. The formation of microcracks due to residual shrinkage stresses and the interactions of the crack front with dispersed particles may lead to increased fracture toughness in particle filled composites. The creation of new fracture surfaces which includes fibre debonding was found to be mainly responsible for the fracture behaviour of fibre reinforced composites. Although these mechanisms have their individual contributions to the fracture toughness of three phase composites, the addition of particles at high volume fractions may have a detrimental effect on the toughening character of fibre reinforcement.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat